1. Technical Field
The present invention relates to methods and apparatus for welding metal sheets in general, and to methods and apparatus for controlling the gap between the metal sheets being welded in particular.
2. Background Information
Laser welding is now in widespread use as a process for joining metal sheets together. In this process the sheets are preferably butt jointed, with their edges positioned so that there is only a narrow gap between the sheets. To obtain a weld seam of high quality, the gap between the sheets to be joined should not be wider than 0.05 or 0.08 mm, and the deviations of each individual sheet should not exceed one half of these maximum permissible widths of gap. It is obvious that in order to observe such tolerances, correspondingly expensive tools, or complicated machining methods, are necessary.
It is known from European Patent Application No. EP 0565846 when welding straight seams to plastically deform at least one of the metal sheets with a squeeze roller before or in the welding zone so that the maximum permissible width of gap between the sheets to be joined is not exceeded. In connection with this known teaching, a series of embodiments are described which relate in particular to the varied configuration of the squeeze rollers.
The known teaching is only suitable for straight weld seams. In particular it is unsuitable if there is a requirement to guide the weld seams along a given line, as in such cases the squeeze rollers proposed in the known teaching generate lateral forces which can lead to undesired distortions of the metal sheets.
It is, therefore, an object of the present invention to provide a method and an apparatus for welding metal sheets that can weld a seam along any given line.
According to the present invention, an apparatus for handling a pair of sheet metal workpieces to be welded is provided that includes a first workpiece holder, a second workpiece holder, at least one backing element, and at least one squeeze roller. The first and second workpiece holders are positioned so that an edge of one of the pair of sheet metal workpieces is in contact with, or separated a gap from, an edge of the other sheetmetal workpiece. The backing element is disposed on a first side of the sheet metal workpieces, and the squeeze roller is disposed on a second side of the sheetmetal workpieces opposite the first side. The squeeze roller is substantially aligned with the backing element. The squeeze roller is formed as a body symmetrical in rotation. Force selectively applied to the squeeze roller will cause plastic deformation of one of the pair of sheet metal workpieces and thereby cause the deformed sheet metal workpiece to extend into the gap.
The invention has the following advantages: Since a squeeze roller is used which obtains a plastic deformation that is independent of the squeeze roller""s direction of advance on the metal sheet concerned, the weld seam can be guided along any given line without risking insufficient deformation of the sheets to be welded. The method according to the invention and the apparatus for carrying out the method can therefore be used for welding sheets of any desired shape.
When, in a continuation of the invention, the squeeze roller consist of a ball, it moreover becomes possible to obtain an apparatus according to the invention that is extremely compact, as the radius of the bail is greatly reduced in comparison with the outer dimensions of the known squeeze rollers, which means that the force acting on the squeezer ball to yield a given effect can also be reduced.
Lastly, by forming the squeeze roller according to the invention as a ball, it is possible to set the mounting (or xe2x80x9csupportxe2x80x9d) of the squeeze roller at an oblique angle to the plane formed by the sheets to be welded. This leaves the joint line between the sheets freely accessible, so that detection devices can be used to detect the actual width of gap between the sheets in the squeezing zone. The force acting on the squeezer ball can then be adjusted in response to the instantaneous value of the width of the gap.
These and other objects, features, and advantages of the present invention will become apparent in light of the Detailed Description of the Invention.